The present invention relates to an electrical connector for a circuit board, which is to be mounted on a mounting surface of a circuit board with soldering.
Generally speaking, an electrical connector for a circuit board (hereinafter, simply referred to as a connector) is to be mounted on a mounting surface of a circuit board by reflow soldering of the connector thereto while disposing on the circuit board. Upon mounting by soldering, when a conventional connector is heated, deformation of a housing of the connector, such as warping and twisting, may occur due to difference in coefficients of thermal expansion between the housing and the circuit board. For example, when the housing has an outer shape of a rectangular parallelepiped, the housing may undergo deformation such as concave warping, in which both ends of the housing in a longitudinal direction thereof are lifted, or convex warping, in which a middle part of the housing in the longitudinal direction, is lifted.
Once the housing is deformed in this way, in the lifted part of the housing, connecting portions of terminals therein (portions to be soldered to a circuit part on the mounting surface of the circuit board) could come off from the circuit portion. As a result, disconnection may occur between the connecting portions and the circuit portion even after the reflow soldering. In addition, after the reflow soldering, if the melted solder is cooled to a certain temperature (e.g., 220° C.), the solder is hardened before the housing recovers an original shape thereof from the warping. Accordingly, the connecting portions of the terminals are fixed onto the circuit portion of the circuit board, while the housing is still warped. Moreover, once the housing is further cooled to room temperature, the housing will further try to recover the original shape from the warping. As a result, in the soldering parts of the connecting portions of the terminals and the circuit portion of the circuit board, a residual stress is generated, which may results in destruction of the portions that are mounted by soldering.
Therefore, upon mounting the conventional electrical connector onto the circuit board by soldering, it is necessary to minimize the influence of the deformation of the connector produced by the reflow soldering on the soldering parts for the mounting.
Patent Reference: Japanese Patent Application Publication No. 2011-060590
In the conventional electrical connector described in Patent Reference, a sheet metal member is attached on an upper surface of the connector, which is on the side opposite to the mounting surface. In this state, the connector is mounted on the circuit board by soldering, so that it is achievable to surely restrain the warping of the housing. More specifically, the sheet metal members have flexible portions in areas that correspond to both ends of the rectangular parallelepiped housing in the longitudinal direction. The flexible sections can easily flex in their sheet-thickness direction. Upon mounting the connector on the circuit board by soldering, when the both ends of the housing are heated and become lifted, it is achievable to restrict the warping of the housing with a counterforce (a spring force) that works downward to the ends from the flexible portions.
In the conventional electrical connector disclosed in Patent Reference, upon mounting the conventional connector by soldering, it is necessary to separately provide the sheet metal members having the flexible portions, and remove the sheet metal members after the mounting by soldering. In addition, there remains the difference in the coefficients of thermal expansion between the housing of the connector and the circuit board. Therefore, it is still necessary to avoid generation of the stress that lifts the both ends of the housing upon mounting the conventional connector to the circuit board by soldering. For this reason, when the stress generated at the both ends becomes excessive, for example, due to a material, shape, etc. of the housing of the connector, there is a concern of not being able to restrict the warping of the housing even with the flexible portions of the sheet metal members.
In view of the problems described above, an object of the invention is to provide an electrical connector for a circuit board, which can minimize the deformation of the connector upon mounting by soldering, which is caused by a difference in coefficients of thermal expansion between the connector and the circuit board. As a result, it is achievable to satisfactorily keep the state of the terminals being mounted by soldering on a circuit portion of the circuit board. In addition, it is not necessary to use the sheet metal members as described in Patent Reference.
Further objects and advantages of the present invention will be apparent from the following description of the present invention.